The invention relates to a method for controlling the start-up of a vehicle comprising an engine start-stop system. The invention further relates to a data recording medium and to a control device for carrying out the method. Finally, the invention relates to a vehicle comprising this control device.
The engine start-stop system is better known under the term “start and stop.” Subsequently, only the expression “start and stop” is used.
The invention applies particularly to hybrid vehicles. A “hybrid vehicle” is a vehicle whose engine (power train) comprises a internal combustion engine and an electrical machine, each capable of supplying a torque to an output shaft of a crankshaft so as to rotationally drive the driving wheels of the vehicle.
Among these hybrid vehicles, vehicles integrating the “stop and start” technology make it possible to optimize the fuel consumption of a vehicle by stopping the operation of the internal combustion engine when the vehicle is at a standstill, and by restarting the internal combustion engine, for example, when the driver of the vehicle releases the pressure on the brake pedal. The restarting of the vehicle can be in the form of an initial start-up or an assisted start-up.
“Initial start-up” denotes the start-up of the internal combustion engine during which the rotation of the output shaft of the crankshaft is initiated by an electric starter. “Assisted start-up” denotes a start-up of the internal combustion engine during which the rotation of the output shaft of the crankshaft is initiated by a starter alternator.
The starter and the starter alternator are electrical machines that use an electrical source such as a battery. The operation of a starter or of a starter alternator itself is known. Typically, The starter or the starter alternator rotationally drives the output shaft of the crankshaft until a predetermined engine speed has been reached. “Engine speed” denotes a speed of rotation of the crankshaft output shaft expressed, for example, in rotations per minute. Once this engine speed has been established, a controller controls a maximum fuel injection in the combustion cylinders of the internal combustion engine, and then it adjusts the injection so that the engine speed stabilizes. From then on the starter or the starter alternator stops rotationally driving the output shaft of the crankshaft, and the internal combustion engine operates autonomously.
The vehicles that integrate the “stop and start” technology are particularly well suited for driving in an urban environment where the number of starts and stops is important.
In the continuation of this description, the abbreviated term “stop and start vehicle” is used to denote a vehicle that integrates the “stop and start” technology.
Motor vehicles that are known to the applicant comprise a controlled mechanical gearbox (CMG). The term “controlled mechanical gearbox” denotes a gearbox in which the gear change is assisted electronically. This type of gearbox allows an automatic or sequential changing of gears. Typically, in an automatic change, the gear change is managed by an electronic controller. During a sequential change, the gear change is managed by a driver.
These CMGs have the advantage of actuating a gear change only when optimal engine speed and torque conditions are combined. Thus, the extreme cases where the internal combustion engine stalls or runs over-speed are limited.
In this description, the term “engine torque” is used for the torque supplied by the internal combustion engine to the crankshaft output shaft.
During the start-up of a vehicle comprising a CMG, a clutch rotatably connects the crankshaft output shaft to a driveshaft of the driving wheels. Consequently, the driveshaft taps a torque from the crankshaft output shaft in order to cause movement of the vehicle. If the torque tapped by the driveshaft is greater than the engine torque, the internal combustion engine inexorably stalls.
Thus, it is an inherent disadvantage of these controlled gearboxes that it is difficult to control the clutch during the start-up. This disadvantage is particularly problematic in the case of stop and start vehicles where the number of starts is consistent.
In addition, it is necessary to perform the start-up as rapidly as possible.